Brain researchers say the big fluctuations in IQ performance they found in teens were not random — or a fluke.

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Originally published on October 20, 2011 10:50 am

For as long as there's been an IQ test, there's been controversy over what it measures. Do IQ scores capture a person's intellectual capacity, which supposedly remains stable over time? Or is the Intelligent Quotient exam really an achievement test — similar to the S.A.T. — that's subject to fluctuations in scores?

The findings of a new study add evidence to the latter theory: IQ seems to be a gauge of acquired knowledge that progresses in fits and starts.

In this week's journal Nature, researchers at University College London report documenting significant fluctuations in the IQs of a group of British teenagers. The researchers tested 33 healthy adolescents between the ages of 12 and 16 years. They repeated the tests four years later and found that some teens improved their scores by as much as 20 points on the standardized IQ scale.

"We were very surprised," researcher Cathy Price, who led the project, tells Shots. She had expected changes of a few points. "But we had individuals that changed from being on the 50th percentile, with an IQ of 100, [all] the way up to being in the (top) 3rd percentile, with an IQ of 127." In other cases, performance slipped by nearly as much, with kids shaving points off their scores.

Price and her colleagues used brain scans to confirm that these big fluctuations in performance were not random — or just a fluke. They evaluated the structure of the teens' brain in the early teen years and again in the late teenage years.

"We were able to see that the degree to which their IQ had changed was proportional to the degree to which different parts of their brain had changed," explains Price. For instance, an increase in verbal IQ score correlated with a structural change in the left motor cortex of the brain that is activated when we speak.

There are lots of factors that may explain changes in IQ. Though this study did not attempt to nail them down, lots of prior research has found that educational environment is key. Some researchers have found that rigorous academic curricula lead to improved IQ scores.

Teens' personalities, work ethic and the home environments are important, too. "There's a lot of variability in neural development during adolescence and in young adulthood as well," says Stephen Ceci, a professor of developmental psychology at Cornell University.

He says this study should give educators and parents pause. "It should caution all of us against assuming that one low IQ score, at one time, is capturing all that an individual is capable of," Ceci says.

Many researchers still say there's loads of evidence to show that IQ scores do reveal something essential about a child's intellectual gifts. Though increasingly, Ceci says, there's a consensus that one test is not deterministic. It can't accurately assess a person's talents or future potential.

Suppose you could raise your IQ by exercising your brain like a muscle. That's the analogy researchers are using to explain a new study that finds the IQ of teenagers can rise or fall significantly during adolescence. NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: If you know what the word obstreperous means, raise your hand. Obstreperous. Yup. I can't see you out there, but I would bet all of you straight A types are waving your hands. You were paying attention in school.

So what does this have to do with the story? Well, there was a time when a child's IQ was thought to be a fixed and stable measurement of intelligence, that captured a kid's intellectual potential, if you will. So a teen who could use fancy words like obstreperous would score well on intelligence tests. Stephen Ceci is a psychologist at Cornell University.

STEPHEN CECI: So obstreperous would be - a group of words like obstreperous would be highly predictive of how people would do on the vocabulary part of an IQ test.

AUBREY: Now, a strong vocabulary, Ceci adds, is the result of acquired knowledge, how much you've read or been taught at school and home. And in any given child these skills were thought to develop fairly consistently. How a kid performed at six would hold steady at age 12 or 18, even as tests get harder.

But in recent years, this theory has unraveled a bit. Ceci says a slew of studies show kids' performances on IQ tests can vary. Sometimes it's the academic environment that changes or sometimes kids are just late bloomers.

CECI: The timetable does get highly individualized for kids, and there's a lot of variability in neural developments during adolescence.

AUBREY: The most recent evidence is published this week in the journal Nature. Researchers at the University College London administered IQ tests to a group of healthy schoolchildren between the ages of 12 and 16. And then they repeated the tests four years later. Researcher Cathy Price says she expected to see IQ's inching up or down a few points, but what she documented were dramatic fluctuations.

CATHY PRICE: We had individuals that changed from being on the 50th percentile, you know, with an IQ of 100, right the way up to being on the third percentile with an IQ of 127.

AUBREY: Now, we're only talking about 33 kids here. So it's not clear that this could be true for all teens. But to confirm that these swings were not random or just a fluke of kids having a particularly good or bad day, the researchers did MRI scans of the teens' brains.

PRICE: We looked at the structure of their brain in early teenage years and in the late teenage years. And we were able to see that the degree to which their IQ had changed was proportional to the degree to which their different parts of their brain had changed.

AUBREY: This means that the brain really does change in line with teens' emotional and intellectual development. There are lots of factors that may explain changes, though this study did not attempt to nail them down. Cornell's Stephen Ceci says prior research has shown that rigorous academics can lead to improved IQ scores, similar to prepping for the SATs. Teen personalities, work ethic and the home environments are important too. Some teens are just defiant or obstreperous at age 13, but by 19 or 20 they've dialed in.

CECI: Studies like this one should definitely caution all of us against assuming that that one low IQ score at one point is really capturing all that that individual's capable of.

AUBREY: There's still plenty of evidence that over time IQ tests do measure something innate about a person's intellectual gifts. But there's emerging consensus that, particularly in the teen and young adult years, intellectual development is a bit like physical exercise. The harder you push your brain, the more you have to show for it.